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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Circadian Rhythms of Isoprene Biosynthesis in Grey Poplar Leaves¹

Forschungszentrum Karlsruhe GmbH, Institut für Meteorologie und Klimaforschung, Atmosphärische Umweltforschung, 82467 Garmisch-Partenkirchen, Germany

Isoprene (2-methyl-1,3-butadiene) emission varies diurnally in different species. In poplar (Populus spp.), it has recently been shown that the gene encoding the synthesizing enzyme for isoprene, isoprene synthase (ISPS), displays diurnal variation in expression. Working on shoot cultures of Grey poplar (Populus x canescens) placed under a different light regime in phytochambers, we showed that these variations in PcISPS gene expression, measured by quantitative real-time polymerase chain reaction, are not only due to day-night changes, but also are linked to an internal circadian clock. Measurement of additional selected isoprenoid genes revealed that phytoene synthase (carotenoid pathway) displays similar fluctuations, whereas 1-deoxy-D-xylulose 5-phosphate reductoisomerase, possibly the first committed enzyme of the 1-deoxy-D-xylulose 5-phosphate pathway, only shows light regulation. On the protein level, it appeared that PcISPS activity and protein content became reduced under constant darkness, whereas under constant light, activity and protein content of this enzyme were kept high. In contrast, isoprene emission rates under continuous irradiation displayed circadian changes as is the case for gene expression of PcISPS. Furthermore, binding assays with Arabidopsis (Arabidopsis thaliana) late elongated hypocotyl, a transcription factor of Arabidopsis involved in circadian regulation, clearly revealed the presence of circadian-determining regulatory elements in the promoter region of PcISPS.

² These authors contributed equally to the paper.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Sandrine Louis (sandrine.louis{at}imk.fzk.de).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.092759

^* Corresponding author; e-mail sandrine.louis{at}imk.fzk.de; fax 49–8821–73573.

Received November 7, 2006; accepted November 15, 2006; published November 22, 2006.

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